Conventional fiber optic cables include optical fibers that conduct light for transmitting voice, video and/or data. The construction of fiber optic cables should preserve optical performance when deployed in the intended environment while also meeting the other additional requirements for the environment. For instance, indoor cables for riser and/or plenum spaces may require certain flame-retardant ratings to meet the demands of the space. In other words, these flame-retardant ratings are addition to mechanical requirements or desired characteristics for the space. Mechanical requirements or characteristics such as crush performance, permissible bend radii, temperature performance, or the like are desired to inhibit undesirable optical attenuation or impaired performance during installation and/or operation within the space. In addition to the mentioned requirements riser and/or plenum spaces may require a ruggedized design for meeting the demands of the space.
By way of example, some indoor applications use a fiber optic cable disposed within an armor layer for providing improved crush performance in riser and/or plenum spaces. For instance, conventional armored constructions have a fiber optic cable disposed within a metallic interlocking armor for creating a robust construction. Specifically, one type of well-known metallic interlocking armor is a “BX armor” or a “Type AC” cable. This metal armor is spiral wound about the fiber optic cable so that the edges of the adjacent wraps of armor mechanically interlock, thereby forming a robust armor layer that also acts as a bend limiting feature for the assembly. However, there are disadvantages for this conventional interlocking armor construction. For instance, fiber optic cables having a metallic armor require additional hardware and/or installation procedures for grounding the metallic armor to meet safety standards, thereby making installation time-consuming and expensive.
FIG. 1 shows several prior art examples of interlocking armored cables 10 having a metallic armor layer 12 (typically aluminum) that serves to protect and preserve optical performance of cables 14 therein. Since metallic armor layer 12 is conductive it must be grounded to comply with the National Electrical Code (NFPA 120) safety standard. This adds to the complexity and expense of installing a metal-armored fiber optic cable. Additionally, the metallic armor can be plastically deformed (i.e., permanently deformed) which can pinch the cable and cause elevated levels of optical attenuation. Nevertheless, the market and craft prefer the design and handling of this rugged cabling.
Manufacturers have attempted to design dielectric armor cables to overcome the drawbacks of the conventional metallic armor constructions, but to date a commercial solution is lacking. For instance, U.S. Pat. No. 7,064,276 discloses a dielectric armor cable having two synthetic resin layers where the hard resin layer has continuous spiral groove cut completely through the hard resin layer along the length of the armor. The hard resin layer is intended for bend control by having adjoining edge portions of the spiral groove abut at the desired minimum bend radius. However, one skilled in the art would recognize this design does not provide the craft with all of the desired features. Moreover, it can be difficult for the craft to recognize the cable of the '276 patent as an armored cable layered because it has a smooth outer surface, whereas conventional metal armored cables are easily identified by the craft as depicted by FIG. 1.
Therefore, there is a need in the art for an armored fiber optic cable with superior mechanical properties that does not require grounding as with metallic interlocking armor, but that also resembles the metallic, interlocking armored cables while providing robust characteristics.